To answer \#6, those sizes likely came about due to what tubing sizes were in use when the change to aluminum frames took hold. The old steel frames were 26.8, 27.2 etc because of the tubing used. Same holds for aluminum, the standard was born because of the tubing that was available for builders to use and it has stuck since then. Carbon offers the freedom of pretty much any seatpost diameter, but I would like to think most have stuck with 30.9 and 31.6 to not anger the standards gods too much :\)
March 14, 2018, 8:13 a.m. - Shoreboy
To answer \#6, those sizes likely came about due to what tubing sizes were in use when the change to aluminum frames took hold. The old steel frames were 26.8, 27.2 etc because of the tubing used. Same holds for aluminum, the standard was born because of the tubing that was available for builders to use and it has stuck since then. Carbon offers the freedom of pretty much any seatpost diameter, but I would like to think most have stuck with 30.9 and 31.6 to not anger the standards gods too much :\)